The invention described herein relates to an assembly-procedure for crawler-tracks utilizing lubricated link-pivots, and to the hinge-assembly created therefor.
Crawler-tracks comprising a number of interconnected right and left and links are by now well known. These links are joined by a hinge-assembly basically consisting of a pivot, or pin, and bushings which rotate around said pin--briefly, each link has two holes: one receiving the pin, and one receiving the bushing, these being forced onto the ends of the pin forming part of one hinge-assembly, and of the bushing of another hinge-assembly, respectively. In the first such pairing the link is an outer-link (or outer link-portion), and in the second, an inner link (or inner link-portion). Every crawler track comprises a plurality of such hinge-assemblies disposed in succession and joined together by the links--these being fixed immovably to said hinge-assemblies.
Thus, each set of links basically comprises: a pin, two outer links forced onto the ends of same, a bushing, or sleeve turning coaxially with the pin and occupying its central stretch, and two inner links similarly forced onto the sleeve; a tread then fitted to each composite link is made fast either to the inner or outer pair thus constituted. In this way, one has a situation where each link is connected to two successive assemblies, functioning as inner portion for the one, and as outer portion for the next.
One present-day type of crawler track makes provision for the breasted surfaces of pin and sleeve to be lubricated with oil during operation, with the basic purpose in view of prolonging the track's service life, lowering noise-levels, and increasing efficiency. In order to bring such lubrication about, normal tracks of the type have an oil reservoir located inside the hinge-pin itself which feeds to the breasted surfaces aforesaid by way of one or more radially disposed holes. To prevent leakage and subsequent loss of the lubricant, one has seals located in recesses of annular shape let into the inner surfaces of the outermost links and disposed coaxially with the pin-hole in same; these seals being compressed axially to a given pre-load value, between the annular recess and the butt-end of the sleeve, guaranteeing thus tha no lubricant may leak out from that particular area. In addition, there can be no leakage-out of the lubricant along the pin-ends since these are force-fitted to the outer links. With this arrangement, the oil is obliged to remain where it is in fact supposed to remain--i.e. in the laminar interspace existing between the breasted surfaces of pin and sleeve, as aforedescribed.
A further feature often incorporated into these tracks is that of thrust-rings positioned together with the seals aforementioned in said annular receses, lodged between the outer link and the sleeve butt-end, whose purpose is that of inhibiting axial slide between pin and sleeve, as far at is mechanically possible.
Normally speaking, production-line assembly of lubricated crawler track links involves a series of separate and successive cycles which comprise the following stages:
a preparation of the hinge-assembly by introduction of the pin into its sleeve, and fitting of thrust ring to the pin adjacent to the sleeve butt-ends; PA1 a' location by hand of the oil seals, either in the outer-link recesses or over the pin-ends; PA1 b force-fitting of a pair of inner links over the sleeve-ends, exerting said force from the outsides of the hinge-assembly toward the centre, parallel with the pin-axis; PA1 c force-fitting of a pair of outer links over those pin-ends protruding beyond said sleeve-ends, exerting said force from the outsides of the hinge-assembly toward the centre and parallel with the pin-axis; PA1 d checking for a tight seal such as to render the interspace between said breasted pin and sleeve surfaces totally hermetic; PA1 e injection of oil into the reservoir offered by the hinge-pin. PA1 a hinge-pin whose ends are force-fitted into respective hoels offered by two links; PA1 a sleeve disposed coaxially with and about the central section of said pin, whose ends are force-fitted into holes offered by two further links; PA1 two thrust-rings associated coaxially and as one with said pin adjacent to the butt-ends of said sleeve, and offering housings to said sleeve butt-ends; PA1 sealing means located in said housings, designed to prevent egress of lubricant at said sleeve butt-ends; PA1 a preparation of said hinge-assembly, composed of said pin, said sleeve, said thrust-rings, and said sealing means; PA1 b filling of the hinge-pin reservoir with lubricant; PA1 c a pause of sufficient duration to establish possible oil-leaks from the assembled and lubricated hinge-assembly; PA1 d force-fitting of two inner link bosses to the ends of said sleeve, said force exerted from the outsides of said hinge-assembly and directed toward the center of same parallel with the pin-axis; PA1 e force-fitting of two outer link bosses to the ends of said pin, said force exerted likewise from the outsides of said hinge-assembly and directed toward the center, parallel with the pin-axis.
In effect, stages b and c are carried through by machine--since force-fitting of the links onto the hinge-assembly calls for enormous mechanical pressure--and it will normally be the case that the outer links of one hinge-assembly are pin-ended simultaneously with the inner links of the next hinge in line, which by definition will be sleeve-ended. Stages d and e are carried out on already-assembled composite links a little further down the the same line whilst further links continue to be assembled via stages b and c.
This procedure has a serious disadvantage: i.e. should it be discovered during the stage d that a less-than adequate seal is being provided for one reason or another (poor fitting, or defective material), than the entire plant must be shut down, halting assembly, and dismantling the links one by one from their hinge-assemblies until the initial defect is discovered; which also signifies rejection of a good number of individual components--pins, links, etc.--which may suffer damage when being taken apart. Clearly, considerable losses are involved here, whether of time, energy, or materials.
A worse disadvantage yet in relation to the same defect, is that of an oil-leak being discovered after the track has been fully assembled--in which case the track must be laid out on appropriate plant providing for its disassembly from one end link by link until the defective area is arrived at. It is worth adding at this point, that if the track has been rolled, the defective hinge-assembly will be difficult to locate in the first instance. The loss of time and materials in this case is even greater--moreover, a crawler track presents the handling problem of dead weight, perhaps hundreds of pounds, often over a thousand.
A further drawback stems from the fact that both sleeve and thrust rings are free to slide with respect to the hinge-pin, and must therefore be fitted up a short a time as possible before full assembly of the track. In most instances, such parts are warehoused separately, and covered with a thin film of oil so as to prevent rusting (particularly important in the case of the mating surfaces of pin and sleeve). Thus one has an added inconvenience in that individual hinge components must be treated before going into stock, and then cleaned once again before being used so as to remove both the oil, and dust which will have clung thereto in the meantime--the same applying for the links.
A further drawback arises from the fact that the thrust rings are not force-fitted to crawler track hinge-pins, meaning that oil-seal at the pin end is provided by the latter's pairing with its outer links. This calls for faultless machining both of the pin ends and of the links' pin hole surfaces, with no marks or ridges, if an efficient oil-seal is to be obtained.
The main object of the invention described herein is that of eliminating the disadvantages and drawbacks aforedescribed, most especially those concerned with the discovery of oil-leaks, whether during assembly or following completion of the assembled track.
A further object of the invention is that of providing a hinge-assembly suitable for warehousing in its assembled state, ready-lubricated, and capable of affording its own protection against rust and dirt to the mating surfaces aforesaid.
Another object of the invention is that of avoiding the necessity for an oil-seal afforded by the outer-link-and-pin pairing, thus reducing the amount of precision required in machining such parts, and dispensing with irrational cleaning of both links and hinge-assemblies immediately prior to their being joined together.
Yet another object of the invention is that of setting forth a hinge-assembly easily put together utilizing a small, simple, and perhaps automatically-operated press.
Another object of the invention is that of making for easy introduction of the lubricant into the hinge-pin, since this in fact takes place prior to assembly of the track, making the process simpler.
Another object of the invention is that of permitting a surer discovery of possible oil-leaks from the track's hinge-assemblies.
Another object of the invention is one of offering a hinge-assembly with spare-part usefulness, capable of being fitted to an existing track, and requiring no complicated or costly lubricant-injection equipment.
Another object of the invention is that of creating a hinge-assembly suitable for pairing with the links of non-lubricated tracks, whether new or already used.